Expanded cans

ABSTRACT

Metal can blanks comprising a cylindrical side wall expanded by any known method so that the side wall of the resultant can includes a regular pattern ( 2 ) of individual pattern elements. In one example the pattern elements are diamond in outline and are formed over a central region of the can side wall by about 2.25% expansion. Further expanded margins ( 3, 4 ) are provided above and below this pattern. The pattern elements are arranged in rows and columns so that the pattern comprises at least two rows and at least two columns.

BACKGROUND OF THE INVENTION

This invention relates to expanded cans. In particular it relates to acan having a cylindrical side wall with a regular pattern of expandedelements. The cylindrical can side wall has either an integral base anda single can end (as in a so-called “two-piece” can) or is closed atboth ends (as in a so-called “three-piece” or an aerosol can).

Cans having a patterned side wall have been produced in order to improveresistance against deformation by external pressure. These known canshave pattern elements which are pressed into the side wall of the canblank in order to provide improved axial load or panel performance.Since the elements are only provided for structural reasons, any“pattern” is often covered by a product label. In any case, these canshave only achieved limited shape definition, i.e. a shape which isclearly visible to a consumer, and reduce the capacity of the can of aparticular aspect ratio.

EP-A-0 441 618 describes cans having patterned side walls which aretypical of those referred to above. The pattern elements of EP-A-0 441618 are formed entirely by pressing inwardly on the can side wall suchthat the pattern elements are externally concave with their sides beingat the original side wall diameter.

U.S. Pat. No. 3,335,902 describes superimposed axial and circumferentialbeading rather than pattern elements.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a metal can formedfrom a can blank having at least a cylindrical side wall, the side wallof the can comprising a regular pattern of individual polygonal patternelements, in which: the pattern elements are arranged in at least twocircumferential rows and at least two longitudinal columns; and eachpolygon comprises between 3 and 10 sides; characterised in that: atleast some of the pattern elements are formed by expanding thecylindrical side wall of the can blank so that the can side wall extendsbeyond its original radius, each such expanded pattern element having anexternally concave radius around its edges and an externally convexradius adjacent the concave radius, towards the centre of the patternelement; in which the concave radius is substantially constant aroundthe element; the size of the convex radius is directly proportional toits distance from the centre of the pattern element; and the expansionof any point on an expanded pattern element is inversely proportional toits distance from the centre of the pattern element.

The Applicant has found that cans according to the present inventionhave great visual impact without reducing the can capacity of aparticular aspect ratio. Furthermore, by varying the convex radiusaccording to its distance from the centre of the element, splitting ofthe can side wall, especially at any corners of the pattern element, dueto expansion is substantially avoided whilst maintaining definition ofthe pattern element shape.

In a preferred embodiment, any of the pattern elements may include, inaddition to one or more expanded regions, one or more parts which areformed by depressing the cylindrical side wall of the can blank. Thesides of the pattern elements may be at the original can side walldiameter.

Alternatively, the pattern elements may be curved in outline, forexample tear drop shaped, circular, etc.

In one embodiment, when the pattern element is viewed in plan, the sidesof any of the pattern elements are linear, curved, or comprise a complexcurve. The sides of any of the pattern elements may meet at a radius,the maximum size of which is preferably directly proportional to thesize of the pattern element.

The individual pattern elements may touch or overlap each other, or maythemselves be separated by spaces either longitudinally orcircumferentially or both. One or more spaces between columns of patternelements may be provided for a logo, print or label.

The patterned side wall may be expanded by anything from 2% to 20%,dependent on pattern element size. Where the can blank has an integralbase and side wall, as in a so-called two-piece can, the expansion ispreferably not greater than 10%. The maximum expansion for a two piececan is limited by the degree of work hardening of the can side wall. Thecan blank is usually formed from aluminium or steel or alloys of eitherof these. The can blank side wall may be between 0.075 mm and 0.15 mm inthickness if made of aluminium, typically about 0.1 mm. If the can blankis of steel, the thickness of the side wall may be between 0.06 mm and0.18 mm, typically about 0.08 mm. The closed and pressurised can maywithstand up to 7 bar without pattern reversal. By pattern reversal ismeant that radially inwardly extending parts of the pattern are pushedoutwardly by pressure inside the can. This at least diminishes patterndefinition and at worst, over 7 bar internal pressure, may result inbuckling and/or loss of any visual pattern at all.

In one embodiment, the rows of pattern elements are out of phase witheach other such that elements of adjacent rows are displacedlongitudinally.

The patterned elements may be positioned anywhere on the can side walland it may be preferred to include a margin at either or both ends ofthe side wall. This margin may be the same diameter as the original canblank side wall or may be expanded in the same way as the pattern.

Can expansion may be achieved by any of a variety of known methods suchas by using an expanding mandrel, fluid jets, a roller device whichrolls around and/or up the inner side wall, or by fluid pressure in aclosed can. This last is sometimes referred to as blow forming the fluidis air. In some cases, particularly blow forming, the can is expanded tothe shape of a mould.

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a can having a first pattern;

FIG. 2 is an enlarged developed view of an element of the pattern ofFIG. 1;

FIG. 3 is a developed side view of a second embodiment of patternelement; and

FIG. 4 is a section through the pattern element of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a can body 1 having a side wall with a regular expandedpattern 2 of diamond-shaped elements in a central region and upper andlower expanded regions 3 and 4. The diamond pattern 2 comprises sixcircumferential rows, hereafter referred to as “layers”. There are fourlayers 5 having complete diamonds, the extreme layers 6,7 being partialelements which are blended into the side wall above or below the patternrespectively. The pattern extends around the whole circumference of thecan body, thereby comprising fifteen complete diamond pattern elements.

In the example shown, the can body blank has a cylindrical side wall of66 mm diameter. This has been expanded in the centre of the diamonds ofthe patterned region 2 by 2.25% and in the upper and lower regions 3,4by 8%. The expansion method of the example was by pressurised fluid suchas air. Larger expansion of the pattern elements would be achievable bydifferent expansion methods without splitting the can side wall.

FIG. 1a shows the curvature of the pattern elements as a section throughX—X of the can side wall, passing through the centre of two patternelements 10. In this example, it can be seen that the longitudinalcentral axis L of each diamond is a smooth continuous externally convex,i.e. expanded, curve having a radius R_(L) of 56 to 57 mm. This curve isblended into a “flat” F, i.e. the original diameter cylindrical sidewall, by an externally concave radius R_(F) of 1 mm.

A side wall of a diamond pattern element 10 of FIG. 1 is shown in FIG.2. This diamond has straight side walls 11, 8.5 mm in length 1 _(s),which meet at radii r of approximately 2 mm, typically 1.96 mm. The sizeof these radii r depends on the size of the pattern element, since theelements in this example are small so as to obtain 15 elements aroundthe can circumference, the radii r must be correspondingly small inorder not to lose the definition of the pattern element. If these radiiwere much larger for this size of element then the element would notappear to be diamond-shaped. The axial length 1 _(a) of each of thecomplete diamonds is 19.25 mm.

The depth of the diamond pattern element may vary along each side sothat there is less deformation of the metal of the can at the “corners”12 where the sides of the pattern elements meet. This depth variation isachieved by varying the size of the convex radius R_(L) in directproportion to its distance from the centre of the pattern element. Sincethe corners 12 are further from the centre than are, for example, thecentres of the sides, the value of R_(L) is greater at the corners andthe deformation consequently less severe.

FIGS. 3 and 4 show one of many alternative embodiments of patternelement which are within the scope of the present invention. Thispattern element 20 is hexagonal in shape and may comprise part of aregular pattern comprising anything from two such elements around thecan circumference up to as many as ten or even more. It will beappreciated that the definition of the shape of the pattern elementswill diminish as more are provided around the can side wall since themaximum amount of expansion possible without risk of splitting willdecrease as the number of pattern elements increases. The expansionmethod will also dictate the amount of expansion possible without damageor failure.

In a second example of the present invention, two hexagonal patternelements 20 as shown in FIGS. 3 and 4 were provided around a 66 mmdiameter can body so that effectively two columns of pattern elementswere formed. The side wall of the can body was completely covered by thepattern, leaving no margins either end as in the example of FIGS. 1 and2. This resulted in a regular pattern of two and a half layers ofhexagons, one half hexagon being at the can base end in one column andthe other half hexagon being at the top of the second column.

These large hexagons were formed with 5% expansion. As in the firstexample, this expansion was achieved by pressurised fluid but largeramounts of expansion, depending on the expansion method and metal of thecan body would be possible.

A side section through the line Y—Y is shown in FIG. 4. As can be seenfrom this figure, the pattern elements 20 are expanded to a relativelysmooth curved central section which may have comprise a curve having aconvex radius R_(h) which varies from 95.5 mm to 1990 mm and is blendedinto groove-like areas between pattern elements by a convex radius R_(b)of typically about 8 mm, depending on the amount of expansion. A valueof 4 mm, for example, would also provide satisfactory patterndefinition. The “grooves” themselves comprise an externally concaveradius R_(g) of typically 2 mm. It is considered likely that a grooveradius of less than 2 mm would risk splitting of the can if the can wereexpanded by air pressure. It should be appreciated that the “base” ofthe groove constitutes the side of hexagonal pattern element 20 and isat the original can diameter.

The sides 21 of the pattern elements in this example comprise Beziercurves when viewed in plan but other complex curves could be used. Thesides 21 meet at a radius which is constantly varying but at the actualcorner 22 is about 5 mm. A typical axial length L_(h) for the hexagonalpattern elements of this example is 45.25 mm.

It will be appreciated that although two specific examples of patternhave been described, numerous alternatives are possible within the scopeof the invention. The degree of expansion of the pattern elements mayvary in many respects such as the area of individual elements, theexpansion method, the can diameter and wall thickness or the material ofthe can body. Similarly, the curvature of the side wall after suchexpansion may be varied, particularly where a mould is used, so that anytype of curvature, simple or complex, or indeed flat, i.e. constantdiameter over a length of side wall is possible within the scope of theclaims.

Although a preferred embodiment of the invention has been specificallyillustrated and described herein, it is to be understood that minorvariations may be made in the apparatus without departing from thespirit and scope of the invention, as defined the appended claims.

What is claimed is:
 1. A metal can formed from a can blank (1) having atleast a cylindrical side wall, the side wall of the can comprising aregular pattern (2) of individual polygonal pattern elements (10,20), inwhich: the pattern elements (10,20) are arranged in at least twocircumferential rows (5,6,7) and at least two longitudinal columns; andeach polygon (10,20) comprises between 3 and 10 sides; characterised inthat: at least some of the pattern elements (10,20) are formed byexpanding the cylindrical side wall of the can blank so that the canside wall extends beyond its original radius, each such expanded patternelement having an externally concave radius (R_(F),R_(g)) around itsedges and an externally convex radius (R_(L),R_(h)) adjacent the concaveradius, towards the centre of the pattern element; in which the concaveradius (R_(F),R_(g)) is substantially constant around the element; thesize of the convex radius (R_(L),R_(h)) is directly proportional to itsdistance from the centre of the pattern element; and the expansion ofany point on an expanded pattern element is inversely proportional toits distance from the centre of the pattern element.
 2. A can accordingto claim 1, in which any of the pattern elements includes one or moreparts which are formed by depressing the cylindrical side wall of thecan blank.
 3. A can according to claim 1, in which the sides of any ofthe pattern elements are linear, curved, or comprise a complex curve. 4.A can according to claim 1, in which the sides (11,21) of any of thepattern elements meet at a radius (r,r_(h)).
 5. A can according to claim4, in which the maximum size of the radius (r,r_(h)) is directlyproportional to the size of the pattern element.
 6. A can according toclaim 1, in which the maximum side wall expansion is from 3% to 20%. 7.A can according to claim 6, in which the can is a two-piece can and theexpansion is between 2% and 10%.
 8. A can according to claim 1, in whichthe can is made of aluminium or aluminium alloy and the side wall isbetween 0.075 mm and 0.15 mm in thickness, typically about 0.1 mm.
 9. Acan according to claim 1, in which the can is made of steel or a steelalloy and the thickness of the side wall is between 0.06 mm and 0.18 mm,typically about 0.08 mm.
 10. A can according to claim 2, in which thesides of any of the pattern elements are linear, curved or comprise acomplex curve.